TACONIC SYSTEM IN MICHIGAN. 101 



of the Taconic system. Yet in a region where igneous action lias been so rife, and where, 

 as has been stated in the preceding pages, plutonic rocks are ready to meet the observer 

 on all sides, it would not be safe to infer the place of any of the limestones without an 

 actual examination. In this case I should have been right in locating the rock in the 

 Taconic system without oh examination ; for only a mere inspection was required to see 

 its identity with thai ai Camden, and its equivalency with that of Stockbridge, the special 

 type of this species. I do not deem it at all necessary to repeat the characters of the rock ; 

 but it is proper to say, that like the same mass at Camden, it has suffered by intrusive 

 rocks. One of the quarries is traversed by a huge dyke of greenstone, which remains an 

 upright wall about fifteen feet thick : its direction is N. 40° E. The slates in connection 

 are the magnesian : their strike is northeast, with a curved dip to the southeast. 



VI. THE TACONIC SYSTEM IN MICHIGAN. 



INFORMATION FROM DR. DOUGLAS HOUGHTON, RELATIVE TO THE DEVELOPMENT OF THE 



TACONIC SYSTEM IN MICHIGAN. 



After the preceding pages were ready for the press, I received from Dr. Houghton the 

 interesting information that this system is well developed in the State of Michigan. I 

 give here the account which he obligingly furnished me of the rocks in question. 



The Taconic system is largely developed in the western and central parts of the upper 

 peninsula of Michigan. The slates of the formation are finely exposed along the western 

 boundary on the line of the Menomene river, which cuts across the formation. East of 

 this, and near Lake Superior, the granular quartz makes its appearance in hills of an 

 elevation of several hundred feet. This formation trends northeasterly, and probably in 

 a direction nearly parallel with that in New-York. I am not furnished with details in 

 regard to the separate, or subordinate masses. It is interesting to find the same rocks in 

 so many independent fields ; and I may add, for the purpose of dispelling doubts in regard 

 to the identity of the slates of the peninsula of Michigan and New-York, that on showing 

 Dr. Houghton some of the flagging stones of the Taconic slate with fucoidal impressions, 

 they were recognized at once as the same species of fossils he had observed in the slates 

 of the Menomene river. Another fact stated by him is that he has observed many locali- 

 ties where the slates of the Taconic system pass beneath the Potsdam sandstone, the 

 oldest rock of the New-York system. It would be difficult to add to the weight of this 

 testimony, in regard to the separate and independent existence of a system of fossiliferous 

 rocks of an age anterior to the Silurian or New- York system. 



